Reactions of arenes

Question 1

All reactions of arenes

Answer 1

Combustion
Bromine
Mixture of concentrated sulfuric +nitric acid
Halogenoalkanes and acyl chlorides

Question 2

Combustion in oxygen of benzene

Answer 2

Produces carbon dioxide and water

Question 3

Incomplete combustion of arenes produces?

Answer 3

A sooty flame
Containing unburnt carbon and carbon monoxide

Question 4

Examples of electrophilic substitution

Answer 4

Halogenation (bromine + benzene)
Nitration (mixture of conc sulfuric and nitric acid + benzene)
Friedel crafts reaction (haloalkane/ acyl chloride + benzene)

Question 5

Steps of electrophilic addition mechanism

Answer 5

Curly arrow from delocalised ring of electrons to electrophile
Then: Delocalised ring broken around 1 carbon (has a + inside) and this carbon is bonded to a hydrogen and electrophile now
Then: hydrogen bonded to carbon donates electrons to centre of benzene
Product: benzene with electrophile + a hydrogen ion

Question 6

what must be ensured when the ring of delocalised electrons breaks around a carbon?

Answer 6

The ring doesn’t extend around past the points of the other carbon in the ring

Question 7

Bromine + benzene is also known as?

Answer 7

Halogenation

Question 8

Products of benzene bromination

Answer 8

Bromobenzene
Hydrogen bromine

Question 9

What is the mechanism for bromination of benzene?

Answer 9

Electrophilic substitution

Question 10

How is bromination of benzene electrophilic substitution?

Answer 10

A hydrogen on the benzene ring is substituted by a Br atom
Br+ acts as electrophile

Question 11

Catalyst needed for bromination of benzene

Answer 11

Halogen carrier catalyst
EG FeBr3 or AlBr3

Question 12

What temperature does bromination of benzene occur at?

Answer 12

Room temperature

Question 13

Why is a halogen carrier catalyst required for electrophilic substitution of bromination of benzene?

Answer 13

To polarise the Br2 to produce a Br+ electrophile

Question 14

bromination of benzene equation for polarisation of Br2 by catalyst

Answer 14

Br2 + FeBr3 → Br+ + FeBr4-

Question 15

Electrophile used in bromination of benzene?

Answer 15

Br+

Question 16

Regeneration of catalyst in bromination of benzene

Answer 16

H+ + FeBr4- → HBr + FeBr3

Question 17

Overall equation for benzene bromination

Answer 17

C₆H₆ + Br₂ —–> C₆H₅Br + HBr
(catalyst cancels out)

Question 18

Bromo benzene formula

Answer 18

C₆H₅Br

Question 19

Can halogenation of benzene occur with other halogens?

Answer 19

Yes but the catalyst used must have the same halogen eg FeCl3 for chlorination, like FeBr3 for bromination

Question 20

Benzene + nitric acid is known as?

Answer 20

Nitration

Question 21

Products of benzene nitration

Answer 21

Nitrobenzene (Benzene with NO2 that substituted hydrogen)
Water

Question 22

Nitrobenzene formula

Answer 22

C₆H₅NO₂

Question 23

What is the mechanism for nitration of benzene?

Answer 23

Electrophilic substitution

Question 24

How is benzene nitration electrophilic substitution?

Answer 24

Electrophile used = NO₂+
Substitutes a hydrogen on benzene = nitrobenzene

Question 25

Catalyst used for nitration of benzene

Answer 25

Concentrated sulfuric acid

Question 26

How does concentrated sulfuric acid act as a catalyst in nitration of benzene?

Answer 26

Generates the NO₂+ catalyst

Question 27

Generation of NO₂+ electrophile from catalyst

Answer 27

H₂SO₄ + HNO₃ ------> NO₂⁺ + H₂O + HSO₄⁻

Question 28

Reformation of catalyst in nitration of benzene

Answer 28

H+ + HSO4- → H2SO4 H+ is what was substituted from benzene

Question 29

Nitrating mixture

Answer 29

1 mole concentrated nitric acid to 1 mole concentrated sulfuric acid

Question 30

Overall equation for nitration of benzene

Answer 30

C6H6 + HNO3 → C6H5NO2 + H2O

Question 31

2 Friedel-Crafts reactions

Answer 31

Alkylation Acyltation

Question 32

What is alkylation?

Answer 32

Substitution of 1 hydrogen with alkyl group to benzene by adding haloalkane IN ORDER TO ADD THE ALKYL GROUP FROM HALOALKANE TO BENZENE

Question 33

Does alkylation add the halogen from haloalkane to benzene?

Answer 33

NO To do that: halogenation of benzene using halide pos ion as electrophile

Question 34

Catalyst needed for alkylation of benzene

Answer 34

Halogen carrier catalyst eg AlCl3 or FeCl3 (of any halogen)

Question 35

Generation of electrophile in alkylation from halogen carrier catalyst

Answer 35

R-Cl + AlCl3 → R+ + AlCl4- (can be any halogen)

Question 36

What is the electrophile in alkylation?

Answer 36

alkyl cation eg CH3CH2+

Question 37

Reformation of halogen carrier catalyst in alkylation

Answer 37

AlCl4- + H+ → AlCl3 + HCl

Question 38

Overall equation for alkylation of benzene

Answer 38

C₆H₆ + RX -----> C₆H₅R + HX

Question 39

What is acylation?

Answer 39

Substitution of hydrogen on benzene with an acetyl group by addition of acyl chloride

Question 40

Is the chlorine from acyl chloride added to benzene?

Answer 40

NO Just the acetyl group which is O=C-R Where R is the length of the acyl chloride The carbon bonds to benzene using bond that was bonded to halogen

Question 41

Acetyl group

Answer 41

O=C-R

Question 42

catalyst needed for acylation of benzene

Answer 42

Halogen carrier catalyst FeCl3 AlCl3

Question 43

Electrophile in acylation

Answer 43

O=C-R+

Question 44

Preparing nitrating mixture

Answer 44

Add drop by drop 2cm3 conc sulfuric acid to 2cm3 conc nitric acid in a boiling tube

Question 45

Nitrating mixture + benzene

Answer 45

Added drop by drop Monitor temp below 10 degrees C Leave to stand

Question 46

Why is nitrating mixture + benzene kept below 10 degrees C?

Answer 46

To avoid multiple substitutions of hydrogen on benzene with NO2+ electrophile = avoid a mixture of products

Question 47

Obtaining pure nitrobenzene

Answer 47

Crystallise nitrobenzene by pouring over crushed ice Then purify by recrystallisation: dissolve in hot distilled water solvent suction filter, leave to cool, refilter